Question 64 MODE01 - Chief MODU Engineer

The Correct Answer is A **Explanation of Correct Option (A):** The size (or severity) of a crankcase explosion is primarily dependent on the amount of combustible fuel available and its concentration relative to oxygen (air) within the explosive range. The fuel in a crankcase explosion is the lubricating oil vaporized into an oil mist. For combustion to occur, the concentration of this oil mist to air must fall within the lower and upper explosive limits (LEL and UEL). If the mixture is too lean (below LEL) or too rich (above UEL), an explosion will not propagate effectively, or might not happen at all. When an ignition source (like a hot spot) is present, the intensity of the ensuing explosion is maximized when the mixture is near the stoichiometric (ideal) ratio, which is achieved by having the optimal **ratio of oil mist to air in the crankcase**. **Explanation of Incorrect Options:** **B) The amount of water in the oil in the crankcase:** While water contamination is detrimental to lubrication, it is a non-combustible substance and does not contribute to the fuel source for the explosion. In fact, excessive water vapor could potentially act as an inerting agent, slightly reducing the explosion intensity, but it is not the primary determinant of explosion size. **C) The temperature of the hot spot in the crankcase:** The temperature of the hot spot is the *ignition source* (it determines *if* the explosion starts). Once the mixture ignites, the size and force of the resulting explosion are determined by the energy content of the reacting fuel/air mixture, not the temperature of the initial ignition source. **D) The amount of debris in the oil in the crankcase:** Debris (such as metallic particles) is a contaminant and contributes to wear, which can in turn generate heat and create a hot spot. However, the debris itself does not serve as the primary fuel source for the explosion, which is the oil mist. Therefore, the amount of debris does not directly determine the size of the resulting explosion.